Functional interactions between calmodulin and

estrogen receptor-α

逄雷制作

Introduction ◇ Estrogen receptor signalling

◆Genomic effects Classical

Non-classical

◆Nongenomic effects Ca2+

MAPK/ERK

PI3K/PKB(Akt)

NO

Introduction

◇Estrogen receptor signalling

Introduction

◇ Estrogen receptor signalling

The complexity of ER function is further increased by the existence of cross-talk between the nongenomic and genomic ER signalling pathways.

Introduction

◇ Ca2+/calmodulin signalling

insulin receptor

epidermal growth factor receptor

angiotensin II receptor

G protein-coupled receptors

Introduction

◇ Ca2+/calmodulin signalling

A large body of data supports a fundamental role for calmodulin in

cell proliferation and cell cycle pro-

gression.

Calmodulin and ER

◇Interaction between calmodulin and ER

(i) Calmodulin concentrations are increased in malignant human mammary tissue

(ii) Ca2+/calmodulin stimulates E2 binding to ER

(iii) Calmodulin binds to ER in a Ca2+-dependent manner and this increases the Kd of E2 binding

Calmodulin and ER

◇Interaction between calmodulin and ER

(iv) Ca2+/calmodulin stimulates tyrosine phosphorylation and activation of ER

(v) association of calmodulin with activated estrogen-ER complex increases the interaction of the complex with ERE

(vi) calmodulin is required for the formation of the ER-ERE complex and for activation of an estrogen responsive promotor

Calmodulin and ER

◇Interaction between calmodulin and ER

(i)

(ii)

(iii)

(iv)

(v)

(vi)

★ Ca2+/calmodulin mayparticipate in ER-induced transcriptional activation and the mitogenic effects of estrogen.

Calmodulin and ER

◇ Interaction between calmodulin and ER

E2 administration to ovariectomized mice up-regulated,independently of ER, by 4.5-fold the expression of calmodulin mRNA in the uterus.

Calmodulin and ER

◇ Interaction between calmodulin and ER ◆ Calmodulin has been shown to interact wit

h ER both in vitro and in cells. ◆ Binding is specific for ERα, with no ass- ociation detected between calmodulin and

ERβ.

◆E2 treatment has no significant effect on the interaction.

Calmodulin and ER

◇Calmodulin modulates degradation of ERα

◆ Incubation with the calmodulin antagonists dra-matically decreased the amount of ERα in MCF-7 cell lysates,with essentially no ER protein detected after 16 h incubationwith CGS9343B.

◆ Neither CGS9343B nor trifluoperazine alters the amount of ERα mRNA .

★Calmodulin stabilizes ERα by reducing its degradation.

Calmodulin and ER

◇Ca2+ and calmodulin are necessary for E2-stimulated transcriptional activity of ERα

◆ Incubation of cells with the calmodulin antagonist CGS9343B completely eliminated the ability of E2 to stimulate ERα transcriptional activation.

◆Incubating MCF-7 cells with the cell-permeable Ca2+ chelator BAPTA-AM abrogated E2-induced ERα transcriptional activation.

Putative mechanism of calmodulin in ERα function

A. the interaction of ERα with calmodulin (CaM) and transcriptional coactivators. This complex activates transcription of ERα target genes.

Putative mechanism of calmodulin in ERα function

B.In the absence of calmodulin the conformation of ERα is altered, facilitating its association with corepressors andblocking interaction with coactivators. Gene transcription is thus inhibited.

Putative mechanism of calmodulin in ERα function

A. At normal intracellular calmodulin concentrations,

E2 induces both transcriptional activation and degradation of ERα.

Putative mechanism of calmodulin in ERα function

B. When calmodulin is over expressed, as occurs in breastcarcinoma, ERα degradation is reduced. The increase in the amount of ERαresults in an enhancement of the growth-promoting effects of E2.

Conclusion

◆Calmodulin antagonists inhibit the growth of breast cell lines and augment antiestrogen therapy.

★ The molecular interaction between calmodulin and ERα could be a potential target for novel therapeutic interventions in patients with breast cancer.

The end